The subject invention is directed toward the art of tube fittings and, more particularly, to a tube fitting particularly suited for use with resinous plastic tubing having a high degree of lubricity.
Although it is possible to use standard metal tube fittings for joining plastic tubing, the results achieved are generally somewhat less than desirable. In particular, the relatively high lubricity of the plastic tubing makes it difficult to grip and hold the tubing within the fitting. In addition, when it is desired to have a full, plastic system wherein the fittings are also plastic, the gripping problems are further compounded.
Prior attempts at providing plastic fittings and fittings particularly suited for plastic tubing have taken a variety of different approaches. Often, to generate sufficient gripping forces and prevent tubing collapse, toothed collars and internal tubing sleeves have been used separately or in combination. The internal sleeve approach is undesirable since it tends to reduce the available flow area. Similarly, the toothed collars or ferrules often result in significant deformation and/or damage to the tubing.
Another approach which has been used, comprises driving a tapered, split ferrule into a tapered cam mouth formed about a tube receiving opening in a fitting body. With this prior arrangement there is no ready way to determine when the fitting is properly made-up or to prevent tubing collapse due to over tightening.
Many other fitting designs have been proposed for resinous plastic tube but they have generally suffered from one or more of the noted problems.
The subject invention provides a tube fitting wherein the problems discussed above are overcome and secure gripping and holding of the tube is achieved with a simple and efficient structure. The invention is such that it can be used for either metal or plastic tubing. Likewise, for certain uses and environments the fitting itself can be formed from either metal or plastic.